Operation controls for heating ventilation and air conditioning (HVAC) systems in automobiles often provide tactile feedback to the operator. The feedback represents finite incremental changes or gradients as, for example, the temperature control knob is rotated clockwise from "cold" to "hot." In some applications, instead of a knob, a sliding scale is used which, for example, when moved from left to right provides tactile feedback of finite incremental changes from "cold" to "hot." One common method of providing this tactile, mechanical, feedback is to move a spring steel or plastic ball across a series of detents.
Referring to FIG. 1, there is shown one embodiment of providing tactile feedback in an HVAC detent application. The assembly includes a ball 10 positioned atop a coil spring 14. The ball 10 is held into place by grease 12 or a similar tacky substance such that the stainless steel ball adheres to the spring during handling. The other end of the coil spring is attached, directly or indirectly, to a control knob or sliding indicator. In operation, the ball 10, which can be steel or plastic, will tend to engage a detent 15 due to the biasing force of the spring 14. As the knob is rotated, or slider moved laterally, the ball 10 will engage in each detent 15 with which it axially aligns, thereby providing tactile feedback as each detent 15 contacts the ball 10. The ball, spring, and detent also act to maintain the position of the control indicator.
The prior art ball and spring assembly of FIG. 1 has several drawbacks when used for HVAC system detent applications, however. In particular, the ball and spring can become easily separated when handled or in operation. In addition, the grease required to hold the ball to the spring collects dirt which can reduce the wear characteristics of the ball, particularly in the case of a plastic ball. The grease also has a tendency to contaminate other components of the system and the assembly environment in general. The difficulty in handling the separate ball, spring, and grease assembly also increases the overall assembly costs.